A nuclease from a marine Alteromonas strain is to be further characterized with respect to its physical properties and enzyme kinetic properties while acting upon a variety of nucleic acid substrates. Studies which have shown that the nuclease can cause the cleavage of the DNA helix at the sites of covalent alteration of the helix caused by agents which are known to be carcinogens and/or mutagens will be extended to more compounds, and the detailed kinetics of the enzyme action with regard to certain types of lesions in duplex DNA structure will be determined. Attempts to use the nuclease, in conjuncton with the metabolic activation of procarcinogens and/or promutagens by crude preparations of liver microsomes, to detect damage in duplex DNA caused by the metabolically activated compounds will be carried out. An extensive series of studies to characterize kinetically the exonucleolytic degradation of duplex nucleic acids caused by this nuclease will be done. Experiments have been designed to use the enzyme in quantitation of the equivalent single-strand content of covalently closed circular duplex DNA's having varying numbers of superhelical turns per molecule. Studies will be done which should demonstrate the use of the Ps. nuclease in the removal of the non-base-paired regions from heterduplex DNA. Spectrophotometry, gel electrophoresis, and ultracentrifugation are the major methods which will be used in this work.